Head morphology

To characterize head structure in snakes of Thamnophis melanogaster (crayfish-eating and non-crayfish-eating individuals), Thamnophis eques, Regina grahamii and R. septemvittata, we measured (1) jaw length (distance from the posterior edge of the posterior-most supralabial scale to the anterior tip of the rostrum), (2) head length (distance from the snout tip to the posterior-most portion of the parietal bone), (3) head width (widest part measured while applying pressure on the posterior portion of the head to spread the quadrates and mandibles laterally), and (4) number of maxillary teeth.